Five Weeks on a 100%-Huel Diet

Principal Aims

The purpose of this trial was to evaluate the effect of consuming Huel, a nutritionally complete powdered food, as the sole source of nutrition for 5 weeks. The trial was known as “Project 100”.

The primary goal was to observe physiological markers after 5 weeks consuming Huel, including anthropometric, biochemical, haematological and endocrinological markers. The secondary aim was to receive positive feedback with regard to physical and mental well-being from the post-trial interview.

Background

Project 100 was run by Huel Ltd employees, for Huel. The initial intention for carrying out the trial was for internal use only, in order to acquire further information to support the Huel Nutrition Team’s understanding as to how a total Huel diet affects key blood and anthropometric markers, as well as how people feel when consuming only Huel Powder. However, it was felt that it would be beneficial to share the trial report with the Huel community.

As such, there were interindividual variations with protocol due to limited resource and availability. For instance, not all participants had blood markers measured prior to the trial. As it would not be appropriate to draw conclusions from results where no pre-trial comparisons could be made, it was decided that only results from participants who had all measurements taken would be included in the trial write-up. However, any abnormal results from those that were outside of the core participant group were noted in the discussion. All results are included in the Appendix (pages 5–8).

Method

1. Experimental design

The experimental design was an intervention trial analysing data from Hueligans who have followed a diet comprised entirely of Huel Powder and water for at least 5 weeks, between October and December 2018.

2. Trial population

Nineteen volunteers, men (n=17) and women (n=2), were initially enrolled into the trial, 13 of which completed the 5 week trial. Three of the 19 initial subjects were unable to complete the study because of illness, injury or work commitments. The remaining 3 subjects did not attend blood draw appointments and were presumed to have pulled out of the study. Contact was attempted for each of these subjects to provide clarity about the reason for withdrawal.

Four out of the original 19 volunteers, men (n=3) and women (n=1), had all anthropometric measurements taken pre- and post-trial, and had blood samples taken pre- and post-trial. As such, they were considered the core focus group of this trial (Figure 1). All subjects gave informed, written consent before participating in the trial. Each participant was screened for determination of health status and suitability to partake in the trial. Participants’ Huel usage prior to the trial varied, some never having consumed Huel and some consuming Huel intermittently for 2 years prior to the trial, none of whom had previously completed a 100%-Huel diet.

The majority of participants selected to take part in the trial were from the Huel Private Tester Group, a group that is comprised of individuals who have previously expressed an interest in completing Huel trials and contact details had previously been provided. The remaining participants were contacted directly (via email or as a private message via the Huel UK forum) if they had expressed an interest on Huel social media platforms or the Huel forum about following a diet comprised predominantly of Huel.

Figure 1: Participant information for the 4 core participants

Male

Female

Participant number

1

2

3

4

Age (years)

35

57

37

39

Weight (kg)

73.9

89.6

104.8

83.1

Height (cm)

179

188

175

170.9

Huel usage prior to trial

200 - 400g/day for 1 year

On & off for 2 years

None

6 weeks - 2 meals/day

Instructed Huel calorie intake*

2,600 kcal

1,800 kcal

2,200 kcal

1,900 kcal

Daily calorie deficit*

0

-500 kcal

-500 kcal

-250 kcal

*As explained in the study protocol

3. Study protocol

The assessor provided each participant with a tailored plan of daily Huel Powder (EU v2.3) intake, with their allocated daily calorie intake calculated dependent upon age, height, weight, physical activity and any weight loss, gain or maintenance goals. Information for this was gathered with the Health and Activity Questionnaire Appendix (pages 2–4).

On the first morning of the trial, participants had their pre-trial fasted blood drawn and anthropometric measurements taken. Participants were instructed to consume a diet comprised exclusively of Huel Powder and water for the entire 5-week period. Details of dietary exclusion criteria can be found in the Appendix (page 1).

Participants had their second fasting blood drawn on the subsequent day to ending the 5 weeks of Huel diet.

Upon completion of the trial, participants were instructed to complete a Post-Trial Questionnaire, providing insights into their experience of following a 100%-Huel diet.

4. Measures

4.1. Anthropometry (1)

Participants had their anthropometric data recorded before and after the 5-week trial period by an ISAK accredited trained member of staff. Anthropometric measurements were recorded at roughly the same time for pre and post-trial appointments.

4.1.1. Height and body weight

Height was measured (± 0.1mm) with a seca 213 portable stadiometer (Birmingham, United Kingdom). Subjects were weighed with minimal clothing on a Newline scale (New York, USA). Values were recorded to the nearest 100g.

4.1.2. Body circumferences

The circumference at the upper arm, mid-calf, waist and hip were measured using a flexible, non-elastic measuring tape. The waist and hip circumferences were used to record waist-to-hip ratio as a marker for possible health risks.

4.1.3. Waist-to-hip ratio (WHR)

WHR was estimated by dividing waist circumference by hip circumference (2). The threshold for WHR was >0.9 cm for men and 0.85 cm for women (2), above which the risk of developing metabolic complications was substantially increased.

4.1.4. Body Mass Index (BMI)

BMI was estimated by dividing weight (kg) by height2 (m2) (3). Participants were considered underweight with a result <18.5, normal within the range of 18.5 - 24.9, overweight between 25.0 and 29.9, and obese with a high risk for developing serious health conditions at ≤30 (2).

4.1.5. Sum of 7 skinfolds

Skinfold thicknesses (biceps, triceps, subscapular, supraspinale, abdominal, front thigh, medial calf) were measured to the nearest 1mm, except for low values when results were recorded to the nearest 0.5mm. Skinfolds were measured in triplicate by the same assessor. Measurements were made on the right-hand side of the body using Harpenden Skinfold Calipers (West Sussex, United Kingdom).

4.2. Bloods

Samples of fasting blood were collected by trained phlebotomists at local and approved partner clinics, located near to the participants’ home address. Blood samples were analysed by Medichecks Ltd.

4.3. Health and Activity Questionnaire

A questionnaire was completed by each participant before they started the trial. The questionnaire was divided into three sections including questions pertaining to health and Huel consumption with the final section concerning diet, physical activity and well-being Appendix (pages 2–4).

4.4. Post-Trial Questionnaire

Each participant completed a post-trial questionnaire, giving further information as to their experience of completing the trial, including feedback of energy and stress levels Appendix (pages 9–26).

Results

1. Anthropometric data (see Figure 2)

All participants lost weight at an average of 6.3kg (range of 2.2kg - 9.1kg). Three out of the 4 participants were following a calorie deficit, as per their desire to lose body weight.

All participants recorded a reduction in sum of 7 skinfolds, with the average of 18.58mm (range of 10.6mm - 27.4mm). WHR decreased in all but 1 participant, at an average of 0.03 (range of 0.01 - 0.05). BMI also decreased in all participants with the pre- to post-trial average of 1.98 (range of 0.7 - 3).

Gout markers – Uric acid was reported to exceed optimal range in participants 5 and 7, with results of 424µmol/l and 534µmol/l respectively.

Iron status – Participant 9 had high post-trial total iron results (36.13µmol/l) and transferrin saturation % (62.91%), both of which were above optimal range. This participant had a 3,000-calorie per day Huel intake.

Of the 7 remaining participants, only participant 10 reported higher than optimal range for TC (7.54mmol/l) and LDL post-trial (5.54mmol/l).

Vitamins – Participant 5 had lower than optimal range serum folate at 2.49µg/l pre-trial which increased to 4.53µg/l post-trial. His vitamin D increased from 33.5µmol/l pre-trial to 48.7µmol/l post-trial, although this was still below the optimal range of 50-200µmol/l.

The following is a summary of the key points reported in the Post-Trial Questionnaire by each of the 4 core participants, explaining how they found completing the 5 weeks of 100% Huel. Full Post-Trial Questionnaires for each participant can be found in the Appendix (pages 9–26).

3.1. Participant 1

Although participant 1 reported that the trial was easy to follow and required minimal time to prepare, he found the lack of variety in taste and texture tedious.

3.2. Participant 2

Participant 2 reported that the trial was psychologically difficult to complete as he was continuously hungry, although he theorised that this was due to the calorie deficit. He reported that the main positives of using Huel for 100% of his diet was that his fluid intake increased drastically and the assistance to weight loss.

3.3. Participant 3

In spite of reporting that the lack of taste and texture during the trial was boring, participant 3 reported that using Huel Powder for 5 weeks was beneficial as it allowed him to “reset” his attitude towards food. Before the trial he self-reported that his diet was unhealthy and his goal was to lose fat mass.

3.4. Participant 4

Participant 4 reported that the trial was easy to follow and noticed “increased energy levels” as the trial progressed, even though she was following a calorie deficit. The only negative symptom reported was a “salt taste” in her mouth during the last 4 days of the trial.

During a post-trial phone call, participant 4 also reported that she experienced other symptoms prior to the trial that may be of interest. Even though a phone call was not part of the initial protocol, it was considered that these symptoms should be reported in the results. Participant 4 reported suffering from headaches prior to consuming Huel (she’d been having Huel for one or two meals per day for a few weeks prior to the trial). The headaches returned 2 to 3 days after the cessation of the trial when she was consuming no Huel at all.

All participants reported that they would continue with Huel for one or two meals per day after the trial.

3.5. Remaining participants

The remaining individuals that did not have pre-trial blood results taken and consequently did not have their results reported in the main trial write-up also completed a Post-Trial Questionnaire. The main feedback from these questionnaires was that following a Huel diet for 5 weeks was convenient as it took the decision process away from preparing food. Participants reported that energy levels increased from the start to the end of the trial, and those that set goals at the start of the trial reported that consuming a diet solely of Huel helped them to achieve these goals.

The main negatives reported by these participants was the lack of variety in taste and texture, and that they missed the social aspect of eating conventional meals with friends and family. Gastrointestinal discomfort and related symptoms were reported by 6 out of the 9 participants. The main symptoms were flatulence, diarrhoea and bloating, 3 of which reported that these symptoms ceased within the first week of the trial. Headaches were also reported by 3 participants, all of which noted they stopped within the first week.

One of the participants who withdrew from the study did so in her second week of the 5-week trial due to gastrointestinal discomfort.

Discussion

The 4 core participants completed 5 weeks following a 100%-Huel diet. There were numerous anthropometric and blood marker improvements reported at the cessation of the trial, and all participants reported a generally positive experience.

Anthropometry

Three out of the 4 participants were following a calorie deficit to aid weight loss, all of which achieved this goal by the post-trial analysis.

WHR is a marker for body fat distribution and is a strong independent risk factor for numerous obesity-related diseases such as myocardial infarction, stroke and premature death (4, 5). WHR is considered a stronger marker for these diseases compared with other measures such as BMI (4, 6). All 3 participants that were following a calorie deficit reported an improvement in WHR, thereby decreasing their risk of developing metabolic complications.

The sum of 7 skinfold measurements estimates the percentage of body fat by measuring skinfold thickness at numerous locations on the body (7). All 4 participants showed a reduction in sum of 7 skinfolds post-trial, indicating a loss in subcutaneous adipose tissue.

Although using BMI as a marker does not come without limitations (8), it is used as an additional marker to quantify the tissue mass of an individual, and categorise that individual into either underweight, normal weight, overweight or obese (3). All 4 participants reported improvements in BMI after the 5-weeks’ Huel consumption, 1 of which moved from the ‘overweight’ category to ‘normal’ category.

Blood markers

Participant 1

Participant 1 had slightly raised alanine aminotransferase (ALT) levels pre-trial. Alanine aminotransferase is an enzyme found mostly in the liver and is measured as a biomarker for liver health (9). Results that are lower than 4 times the highest normal level (optimal range is between 0 and 50iu/l) are considered only slightly increased (10). His mild asymptomatic increase in ALT pre-trial is therefore not a concern, especially considering they fell to within optimal range in post-trial.

He also had raised elevated CK levels which was outside of optimal range pre-trial. CK is an enzyme present in muscle, and the most common cause of high CK in the blood is exercise-induced muscle damage, which can result in high CK levels in the blood for up to a week (11). As participant 1 is a physically active individual, his elevated CK results are most likely due to muscle damage.

Participant 1’s results showed lower than optimal range for vitamin C pre-trial, which fell even lower post-trial. We are unable to offer an obvious explanation for this due to the fact that the vitamin C result was out of range pre-trial.

Participant 1 presented with raised uric acid levels after consuming 5 weeks of Huel for 100% of his diet. Uric acid is a waste product produced from the breakdown of dietary purines and is an important antioxidant that helps to prevent free radical damage (12). Chronically high blood levels of uric acid have been associated with gout (12). Huel contains a moderate amount of purines, and as participant 1 was consuming approximately 2,600 calories worth of Huel per day, this may be linked to the elevated uric acid readings.

Participant 2

Participant 2 presented with slightly lower RCC and neutrophil count post-trial. As his results were within range pre-trial and these results typically vary day to day, follow-up results would need to be completed before a conclusion can be made.

Urea is a waste product of metabolism and is measured as a marker for kidney function. Participant 2 showed raised urea levels post-trial, which was above optimal range. Increased plasma/serum urea could be due to an increase in dietary protein (13).

Participant 2 had slightly elevated CK levels but was participating in regular exercise throughout the study and this is therefore most likely as a result of exercise-induced muscle damage (13).

Participant 2’s transferrin saturation decreased during the trial and resulted in a below optimal range at the post-trial blood sample. A lower transferrin saturation percentage is usually reflective of iron deficiency (14), and even though the participants’ post-trial iron levels were not below optimal range, they had fallen compared to pre-trial results.

Participant 3

Participant 3 showed results outside of optimal range for all three kidney function tests prior to completing the trial. These results could be indicative that the kidneys were not functioning as they should. Although there was a clear improvement in kidney function tests following the trial, with his urea and creatinine readings decreasing, this may not be related to Huel consumption.

Similar to participant 1, participant 3’s uric acid levels increased from pre- to post-trial, which is most likely due to Huel’s moderate purine content.

Participant 3 showed a decrease in total cholesterol from pre- to post-trial. His post-trial HDL cholesterol results fell below optimal range at post-trial compared to pre-trial. However, his LDL:HDL ratio, which can be a marker for heart disease, decreased from pre- to post-trial. Generally speaking, the lower this number the more favourable a person’s cholesterol profile. People that are overweight have an increased risk of a high serum cholesterol level and poor LDL:HDL ratios (15). This positive result was likely due to his combined weight loss and the inclusion of monounsaturated and polyunsaturated fatty acids from Huel.

Folate, a B-vitamin, has several important functions in the body including the maintenance of a healthy nervous system (18) and its role in reducing cardiovascular disease risk (19). Participant 3 had a below optimal folate reading pre-trial. However, this elevated during the 5-week trial.

Participant 4

Participant 4 showed slightly low RDW results, outside of optimal range for pre- and post-trial. As her results fell only slightly outside the RDW optimal range of 11.5-14.4%, it was not considered significant.

The white blood cells, monocytes, were reported as below optimal range in the pre-trial blood analysis, which could have been considered a sign of depressed immune function due to an infection. Post-trial analysis showed her monocytes had increased to within optimal range, therefore this was not significant to the trial.

Bilirubin levels, a marker for liver function, increased from pre- to post-trial and as a result slightly exceeded optimal range.

Participant 4’s blood analysis showed that she had numerous cholesterol status readings that fell outside of optimal range pre-trial. Total cholesterol and LDL were both above optimal range and HDL results were slightly lower than optimal range. However, post-trial cholesterol status improved with total cholesterol returning to within ‘normal’ parameters along with LDL. Her HDL remained outside of optimal range post-trial, although similar to participant 3, this could be explained by a favourable decrease of LDL:HDL ratio from pre- to post-trial.

Participant 4’s vitamin C results were below optimal range pre-trial. However, post-trial results showed an increase in vitamin C and her results were considered within range. Huel contains a high level of vitamin C, which may explain the increase in this reading.

Her pre-trial blood results showed slightly low levels of vitamin D, which is not unexpected given that the trial took place between the months of October and December. In the UK, sunlight doesn’t contain adequate UVB radiation in the winter months (October to March) for the body to be able to synthesise active vitamin D (20, 21). However, her post-trial blood results showed an increase in vitamin D, bringing her to within optimal range for this essential vitamin. Huel is high in vitamin D, providing 300% Nutrient Reference Value (NRV) per 2,000 calories of Huel. Even though participant 4 was consuming lower than 2,000 calories of Huel per day, she would still be consuming adequate amounts of vitamin D to meet the NRV.

General trends/findings

In all 4 core participants, the cholesterol profile improved with a decrease in TC and a reduction in the LDL:HDL ratio from pre- to post-trial. Huel is a good source of the soluble fibre, oat beta-glucans, which have been reported to lower blood cholesterol and reduce the risk of developing coronary heart disease (22).

Additionally, the fatty acid profile of Huel could be linked to the positive changes in cholesterol status. It has been reported that when monounsaturated fatty acids, also known as omega-9 fatty acids, replace saturated fatty acids, LDL and total cholesterol decrease significantly (16, 17). Huel is a good source of monounsaturated fatty acids, provided predominantly by the oats, flaxseed and sunflower oil.

As a proportion of total energy intake, a high consumption of polyunsaturated omega-3 and omega-6 fatty acids have also been shown to decrease total cholesterol and LDL (23). Huel is rich in omega-3s, predominantly from flaxseed, and omega-6s, predominantly from sunflower oil, at 15.8g and 15.6g respectively per day (amounts based on Huel Powder v2.3 Vanilla).

Uric acid increased in all 4 participants, 2 of which reported post-trial results that were above optimal range. Although participant 13 was not one of the core 4 participants, it is worth mentioning that he has been consuming Huel for the majority of his diet for 3 years and showed uric acid levels that were within optimal range (“used Huel pretty much 100% for nearly 3 years” – Appendix (pages 25–26).

Post-Trial Questionnaire

Although most participants reported that the trial lacked variety in taste and texture, the arduousness of completing the trial was considered fairly low, with the average difficulty level being reported as 4.5 (on a scale of 1 to 10, whereby 1 was easy and 10 was incredibly difficult). One participant that scored difficulty as 7/8 self-resolved that this was because he was “constantly hungry, but was on a calorie loss.”

Convenience seemed to have been one of the main positives of following a 100%-Huel diet. It was reported that the trial was “easy & accessible” which helped to improve discipline and “make better choices” about food.

One participant reported a salt taste in the mouth in the last week of the trial, a symptom of which cannot be explained without further investigation.

Trial limitations

There were two main limitations of this trial, both of which would be considered if a follow-up trial were to be completed. The most obvious of these would be that all participants would follow the same protocol. Secondly, more of the vitamins and minerals would be included in the blood testing suite, which could not be facilitated in the current trial due to resource.

Summary

Following a 100% Huel Powder diet for 5 weeks resulted in positive anthropometric changes, such as decreased WHR, body weight and skinfold thickness. Together with notable improvements in blood cholesterol status, these results indicate improvements in cardiovascular and other disease risks.

Uric acid was seen to increase when consuming Huel Powder as the sole source of nutrition for 5 weeks. Individuals who are susceptible to gout should take caution if they have a high calorie requirement and are considering using Huel for 100% of their nutritional intake, and it would be preferential to limit Huel to one or two meals/snacks per day.

All 4 participants reported that they found the trial challenging from a socialising perspective when consuming Huel Powder as their sole source of nutrition. However, the convenience aspect helped participants to avoid unhealthy food options, and all reported that they would continue using Huel as a significant part of daily nutrition after the trial.

Huel Powder can be the sole source of nutrition if consumed at an amount of at least 2,000 calories per day, although this is not something that has been actively recommended. The results of this trial support the claim that Huel Powder can safely be consumed as a total nutrition source. Blood marker results illustrate that following a 5-week 100%-Huel Powder diet is likely to offer health benefits. The results of the trial also support the recommendation that people will benefit from including Huel Powder as a convenient meal alternative to less favourable food choices.